feat: add preview_path migration and constants

Task 2: DB Migration
- Add preview_path column to images table via ALTER TABLE
- Migration runs automatically on database initialization
- Handles duplicate column gracefully

Task 3: Constants & Config
- Export PREVIEW_FS_DIR constant (data/previews)
- Export PREVIEW_CONFIG (800px, 85% quality, JPEG)
- Update ImagePreviewService to import from constants
- Update schema.sql documentation with preview_path

backend/src/constants.js

@@ -12,9 +12,20 @@ const endpoints = {
 // Use path.join(__dirname, '..', UPLOAD_FS_DIR, fileName) in code
 const UPLOAD_FS_DIR = 'data/images';
 
+// Filesystem directory (relative to backend/src) where preview images will be stored
+// Use path.join(__dirname, '..', PREVIEW_FS_DIR, fileName) in code
+const PREVIEW_FS_DIR = 'data/previews';
+
+// Preview generation configuration
+const PREVIEW_CONFIG = {
+    maxWidth: 800,        // Maximum width in pixels
+    quality: 85,          // JPEG quality (0-100)
+    format: 'jpeg'        // Output format
+};
+
 const time = {
     HOURS_24: 86400000,
     WEEK_1: 604800000
 };
 
-module.exports = { endpoints, time, UPLOAD_FS_DIR };
+module.exports = { endpoints, time, UPLOAD_FS_DIR, PREVIEW_FS_DIR, PREVIEW_CONFIG };

backend/src/database/DatabaseManager.js

@@ -90,6 +90,17 @@ class DatabaseManager {
             `);
             console.log('✓ Images Tabelle erstellt');
 
+            // Migration: Füge preview_path Feld zur images Tabelle hinzu (falls nicht vorhanden)
+            try {
+                await this.run('ALTER TABLE images ADD COLUMN preview_path TEXT');
+                console.log('✓ preview_path Feld zur images Tabelle hinzugefügt');
+            } catch (error) {
+                // Feld existiert bereits - das ist okay
+                if (!error.message.includes('duplicate column')) {
+                    console.warn('Migration Warnung:', error.message);
+                }
+            }
+
             // Erstelle Indizes
             await this.run('CREATE INDEX IF NOT EXISTS idx_groups_group_id ON groups(group_id)');
             await this.run('CREATE INDEX IF NOT EXISTS idx_groups_year ON groups(year)');

backend/src/database/schema.sql

@@ -24,6 +24,7 @@ CREATE TABLE IF NOT EXISTS images (
     upload_order INTEGER NOT NULL,
     file_size INTEGER,
     mime_type TEXT,
+    preview_path TEXT,  -- Path to preview/thumbnail image (added in migration 003)
     created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
     FOREIGN KEY (group_id) REFERENCES groups(group_id) ON DELETE CASCADE
 );

backend/src/services/ImagePreviewService.js

@@ -1,16 +1,7 @@
 const sharp = require('sharp');
 const path = require('path');
 const fs = require('fs').promises;
-
-// Preview configuration
-const PREVIEW_CONFIG = {
-    maxWidth: 800,
-    quality: 85,
-    format: 'jpeg'
-};
-
-// Preview directory relative to backend/src
-const PREVIEW_FS_DIR = 'data/previews';
+const { PREVIEW_FS_DIR, PREVIEW_CONFIG, UPLOAD_FS_DIR } = require('../constants');
 
 class ImagePreviewService {
     /**
@@ -121,7 +112,6 @@ class ImagePreviewService {
      * @returns {string} Absolute path to original file
      */
     getOriginalPath(fileName) {
-        const UPLOAD_FS_DIR = require('../constants').UPLOAD_FS_DIR;
         return path.join(__dirname, '..', UPLOAD_FS_DIR, fileName);
     }
 
@@ -132,7 +122,6 @@ class ImagePreviewService {
     async cleanupOrphanedPreviews() {
         try {
             const previewDir = path.join(__dirname, '..', PREVIEW_FS_DIR);
-            const UPLOAD_FS_DIR = require('../constants').UPLOAD_FS_DIR;
             const originalDir = path.join(__dirname, '..', UPLOAD_FS_DIR);
 
             // Check if preview directory exists